Add regular polygons to visualize (#1215)

crates/typst-library/src/visualize/polygon.rs

@@ -1,3 +1,5 @@
+use std::f64::consts::PI;
+
 use crate::prelude::*;
 
 /// A closed polygon.
@@ -19,6 +21,10 @@ use crate::prelude::*;
 /// Display: Polygon
 /// Category: visualize
 #[element(Layout)]
+#[scope(
+    scope.define("regular", polygon_regular_func());
+    scope
+)]
 pub struct PolygonElem {
     /// How to fill the polygon. See the
     /// [rectangle's documentation]($func/rect.fill) for more details.
@@ -91,3 +97,71 @@ impl Layout for PolygonElem {
         Ok(Fragment::frame(frame))
     }
 }
+
+/// A regular polygon, defined by its size and number of vertices.
+///
+/// ## Example { #example }
+/// ```example
+/// #polygon.regular(
+///   fill: blue.lighten(80%),
+///   stroke: blue,
+///   size: 30pt,
+///   vertices: 3,
+/// )
+/// ```
+///
+/// Display: Regular Polygon
+/// Category: visualize
+#[func]
+pub fn polygon_regular(
+    /// How to fill the polygon. See the general
+    /// [polygon's documentation]($func/polygon.fill) for more details.
+    #[named]
+    fill: Option<Option<Paint>>,
+
+    /// How to stroke the polygon. See the general
+    /// [polygon's documentation]($func/polygon.stroke) for more details.
+    #[named]
+    stroke: Option<Smart<Option<PartialStroke>>>,
+
+    /// The diameter of the circumcircle of the regular polygon (https://en.wikipedia.org/wiki/Circumcircle).
+    #[named]
+    #[default(Em::one().into())]
+    size: Length,
+
+    /// The number of vertices in the polygon.
+    #[named]
+    #[default(3)]
+    vertices: u64,
+) -> Content {
+    let radius = size / 2.0;
+    let angle = |i: f64| {
+        2.0 * PI * i / (vertices as f64) + PI * (1.0 / 2.0 - 1.0 / vertices as f64)
+    };
+    let (horizontal_offset, vertical_offset) = (0..=vertices)
+        .map(|v| {
+            (
+                (radius * angle(v as f64).cos()) + radius,
+                (radius * angle(v as f64).sin()) + radius,
+            )
+        })
+        .fold((radius, radius), |(min_x, min_y), (v_x, v_y)| {
+            (if min_x < v_x { min_x } else { v_x }, if min_y < v_y { min_y } else { v_y })
+        });
+    let vertices = (0..=vertices)
+        .map(|v| {
+            let x = (radius * angle(v as f64).cos()) + radius - horizontal_offset;
+            let y = (radius * angle(v as f64).sin()) + radius - vertical_offset;
+            Axes::new(x, y).map(Rel::from)
+        })
+        .collect();
+
+    let mut elem = PolygonElem::new(vertices);
+    if let Some(fill) = fill {
+        elem.push_fill(fill);
+    }
+    if let Some(stroke) = stroke {
+        elem.push_stroke(stroke);
+    }
+    elem.pack()
+}

tests/typ/visualize/polygon.typ

@@ -8,6 +8,7 @@
 #polygon()
 #polygon((0em, 0pt))
 #polygon((0pt, 0pt), (10pt, 0pt))
+#polygon.regular(size: 0pt, vertices: 9)
 
 #polygon((5pt, 0pt), (0pt, 10pt), (10pt, 10pt))
 #polygon(
@@ -27,6 +28,9 @@
 // Self-intersections
 #polygon((0pt, 10pt), (30pt, 20pt), (0pt, 30pt), (20pt, 0pt), (20pt, 35pt))
 
+// Regular polygon; should have equal side lengths
+#for k in range(3, 9) {polygon.regular(size: 30pt, vertices: k,)}
+
 ---
 // Error: 10-17 point array must contain exactly two entries
 #polygon((50pt,))